lol i think the sisters care for each other and doesnt mind sharing you between them
at leats is the impression that i got when i was playing, especialy the escene in the storage with gracie and isabel,
and i think luna will not be very happy if finds out that you hurt one of her sisters, imagine if luna sees gracie sad because of you
this point is valid aswell for gracie and isabel, even cordia, imagine that cordia finds out that you broke the heart of one of her daughters,
again is the impression i got
you are here to solve the problems of the family and eventually you will reconciliate luna and her mother, you have been helping everyone with their issues
and eventually they will be a big happy family again (obviously with some dificultties in the way) with a new generation of delucas? i dunno
and im pretty sure antonio doesnt care anymore for isabel in a romantic way (if you decide to help them you will be CRUCIAL in their reconciliation, not them)